P-1: Modbus Slave (Server) Programming
Ladder Program
To use a CLICK PLUS PLC as a Serial Modbus slave, you don’t need any special ladder
program. Set up the communication port properly and you just need an End instruction in
the ladder program to put the PLC in Run mode.
To use CLICK PLUS PLC as a Modbus Ethernet Client, the Modbus TCP Server must be
enabled.
To enable the Modbus TCP Server, select the Function tab located in the Navigation window
and expand “Com Port 1 Setup” and double click on Modbus TCP as shown below.
You can add any additional ladder program to let the slave CLICK PLUS PLC control
something by itself. For instance, you may want to shut down the outputs on the slave (server)
CLICK PLUS PLC should it lose communication with the Modbus master (client).
NOTE: The Modbus master can communicate with the Modbus slave CLICK PLUS PLC without any ladder
program. However, output points on the Modbus slave CLICK PLUS PLC cannot be turned on if the PLC
is not in the Run mode. Because of this, we recommend having at least one End instruction and to put the
PLC in Run mode.
P-1
CLICK PLUS PLC Hardware User Manual, 1st Edition, Rev. B – C2-USER-M
4-27
Chapter 4: PLC Communications
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